Modulation of the lipolysis and subsequent antibacterial activity of the fat from black soldier fly (Hermetia illucens) by the combined selection of slaughtering, drying and defatting methods of the larvae

The aim of this study was to evaluate the modulating effect of the processing of Hermetia illucens larvae on the antibacterial activity of the fat related to lipolysis to free fatty acids (FFAs), mainly as lauric acid. Blanching and freezing were compared for slaughtering, oven or freeze-drying for drying, and mechanical pressing or supercritical fluid for defatting. Freezing plus freeze-drying produced the highest FFAs content (21%), mainly as lauric acid (11%). In agreement, freezing plus freeze-drying was also the most effective method to obtain fats with higher antibacterial activity, regardless of the defatting method. The antibacterial activity was significantly more relevant for gram-positive bacteria, having a strain-dependent character. The most effective fat was bactericidal for Listeria monocytogenes and Bacillus subtilis and reduced Staphylococcus aureus growth. Therefore, it is possible to selectively modulate the antibacterial activity of the H. illucens fat due to lipolysis by the processing methods of larvae. This study provides guidance to choose the best mode of processing of H. illucens larvae to selectively modulate the potential use of the lipid coproduct of this edible insect, either from the point of view of food use, which requires methods of processing to yield a high quality (low acidity), or from the point of view of antimicrobial applications, using methods of processing that selectively produce an antibacterial fat (high acidity). Furthermore, the best antibacterial activity demonstrated for fats of H. illucens of poor acid quality is an innovative approach for revalorization of such fats that would fail to meet the quality standard required for food applications.